1. Field of the Invention
This invention relates to assembly and maintenance of gas turbine engines. In particular, aspects of the invention relate to the use of pre-prepared rigid raft assemblies in the assembly and/or servicing of a gas turbine engine.
2. Description of the Related Art
A typical gas turbine engine comprises a number of components and/or systems that need to be attached thereto in order for the gas turbine engine to function in the intended manner. Such systems and/or components include, for example, fluid systems, electrical systems, monitoring systems and various electronic control units. These systems/components may be referred to as auxiliary (or ancillary) components/systems, and/or as engine dressings.
By way of example, FIG. 1 of the accompanying drawings shows a typical gas turbine engine including two conventional wiring harnesses 102, 104, each provided with a respective connector component 106, 108 for connection to circuitry, which may be for example accommodated within the airframe of an aircraft in which the engine is installed. A conventional gas turbine engine such as that shown in FIG. 1 may also comprise a number of fluid pipes 116. Such fluid pipes 116, which may be for carrying any suitable fluid, such as liquid, gas or a combination thereof, may be mounted to the engine at available locations.
Such fluid and/or electrical systems/components are conventionally mounted directly to the engine, often using separate mounts for each system/component. Thus, the various systems/components conventionally form a complex array of pipes, leads, wires connectors and other components, each of which typically requires individually mounting.
With regard to the electrical system, a typical gas turbine engine has a substantial number of electrical components which serve, for example, to sense operating parameters of the engine and/or to control actuators which operate devices in the engine. Such devices may, for example, control fuel flow, variable vanes and air bleed valves. The actuators may themselves be electrically powered, although some may be pneumatically or hydraulically powered, but controlled by electrical signals.
Electrical power, and signals to and from the individual electrical components, are commonly transmitted along conductors. Conventionally, such conductors may be in the form of wires and cables which are assembled together in the harness 102, 104. The connections between the individual components and the conventional harness are made, for example, by the multi-pin plug and socket connectors 106, 108. Similarly, communication between the harness and power, control and signalling circuitry is achieved through a multi-pin connector.
The harnesses 102, 104 are assembled from individual wires and cables which are held together over at least part of their lengths by suitable sleeving and/or braiding. Individual wires and cables, for example those indicated at 110, emerge from the sleeving or braiding to terminate at plug or socket connector components 112 for cooperation with complementary socket or plug connector components 114 on, or connected to, the respective electrical components.
Each conventional harness 102, 104 therefore comprises a multitude of insulated wires and cables. This makes the conventional harness bulky, heavy and difficult to manipulate. The conventional harnesses 102, 104 occupy significant space within a gas turbine engine (for example within the nacelle of a gas turbine engine), and thus may compromise the design of the aircraft, for example the size and/or weight and/or shape of the nacelle.
With regard to the fluid systems, these may conventionally comprise fluid pipes 116 provided to the engine, for example in spaces between the electrical harnesses. The fluid pipes 116 may have separate mounts/attachments to the gas turbine engine. The fluid pipes 116, for example in combination with other engine dressings, such as the electrical systems occupy significant space within a gas turbine engine (for example within the nacelle of a gas turbine engine), and thus may compromise the design of the engine/aircraft, for example the size and/or weight and/or shape of the nacelle.
Thus, the complex arrangement of conventional engine dressings may be difficult and time consuming to assemble and/or attach/remove from the rest of the engine, difficult to manipulate, heavy, and/or bulky.
Furthermore, because conventional engine dressings (including, for example the electrical and fluid systems) comprise a large number of components, including various individual wires and/or bundles of wires, pipes, supporting components (such as brackets or cables) and electrical and/or mechanical connectors, the assembly/disassembly process is complicated (and thus susceptible to errors) and/or time consuming. Thus, in many build and maintenance (or repair or overhaul) procedures on a gas turbine engine, removal and subsequent refitting of the conventional engine dressings may account for a very significant portion of the operation time and/or account for a significant proportion of the potential assembly errors.
Still further, the conventional dressings, such as the fluid pipes and/or the electrical conductors in the conventional harnesses, may be susceptible to mechanical damage. For example, mechanical damage may occur during installation (due to exposed components and/or complicated assembly procedures) and/or during service (for example due to vibration). In order to reduce the likelihood of damage to the conductors in a conventional harness, protection such as sleeves/braiding may need to be reinforced/provided, adding still further weight and reducing the ease with which they can be manipulated.